1. Field Of The Invention
The present invention relates to methods and a device for heating a semiconductor wafer, and more particularly to methods and a device for locally heating a semiconductor wafer having different kinds of impurities.
2. Background of the Invention
A semiconductor device such as a transistor in a semiconductor wafer commonly includes N-type or P-type impurity regions that are formed by implanting impurities into the wafer and heating the wafer to diffuse the impurities. Donor-type dopants, such as phosphorus, are used to form the N-type regions, and acceptor-type dopants, such as boron, are used to form the P-type regions. The electrical characteristics of the semiconductor device are dependent upon the dimensions, such as the depth, the length and the width of the impurity regions.
The dimensions of an impurity region are significantly affected by heat treatment of the wafer as well as the implant concentration and the implant energy of the impurities. For example, high heating temperature or long heating time yields an impurity region having a large area and a deep depth.
One of the conventional methods of heat treatment of semiconductor wafers uses an annealing furnace. The impurities are activated in a temperature ranging from 800xc2x0 C. and 1,000xc2x0 C. In the furnace heating method, the desired heating temperature is reached in a heating time of about 30 minutes.
Another example of the conventional heat treatment is called rapid thermal processing (RTP). RTP is typically performed with a tungsten-halogen lamp and a reflecting plate. The activation temperatures can be reached in less than one minute, which is far more quickly than the furnace heating method.
In the above described conventional methods, the wafer is heated as a whole. Since different impurities have different diffusion rates, the regions of different impurities come to have different dimensions, and it is difficult to obtain the precise dimensions required for the respective regions.
Although control of the implantation depth and concentration of the impurities may be used to provide the required dimensions of an impurity region, it is well recognized that implantation depth cannot be easily controlled especially for the shallow junctions, and lateral diffusion also cannot be easily controlled.
The present invention provides methods and a device for heat treating a semiconductor wafer such that precise dimensions of a plurality of impurity regions for a semiconductor device can be obtained. According to an embodiment of the present invention, a heat treating method for a semiconductor wafer having a first region containing a first impurity and a second region containing a second impurity having a diffusion rate different from that of the first impurity includes heating the first region to diffuse at least the first impurity and heating only the second region to diffuse the second impurity.
The present invention also provides a heat treating method for a semiconductor wafer having a first region of a first impurity and a second region of a second impurity having a diffusion rate different from that of the first impurity. The method includes directing radiation at the wafer, blocking the radiation directed at the first region to prevent the first region from heating, and blocking the radiation directed at the second region to prevent the second region from heating.
The present invention also provides that a local heating method for a semiconductor wafer having a first region of a first impurity and a second region of a second impurity having a diffusion rate different from that of the first impurity. The method includes directing a first radiation dose at the wafer to heat the first and the second regions, directing a second radiation dose at the wafer, and blocking a portion of the second radiation dose that is directed at the first region to prevent diffusion of the first impurity.
The present invention also provides that a device for heat treating a semiconductor wafer having different types of impurities with different diffusion rates. The device includes a heat source that directs radiation at the wafer, and a blocker that blocks the radiation and excludes the radiation from at least a portion of the wafer.
The present invention is better understood upon consideration of the detailed description below and the accompanying drawings.